In a computer system particularly including a plurality of storage devices, storage virtualization for allowing a host computer to recognize a storage area generated by combining storage areas of a plurality of physical storage devices as a virtual storage device has been suggested.
For example, a computer system illustrated in FIG. 7 has been known (e.g., see Japanese Laid-open Patent Publication No. 2003-044421). In this computer system, a plurality of host computers (node devices) 1 and a plurality of physical storage devices 2 are mutually connected via a fibre channel switch (network switch) 3 by using fibre channels, some or all of storage areas of the physical storage devices 2 are combined to constitute a virtual storage device (virtual sharing disk) 5 by a network processor 4 of the fibre channel switch 3, and the virtual storage device 5 is provided such that the host computers 1 can access the virtual storage device 5.
According to such storage virtualization using a fibre channel switch, a user can freely construct a virtual storage device suitable for the application of a host computer. By accessing the virtual storage device, the host computer can advantageously use physical storage devices without being conscious of the storage capacity and connection form of the respective physical storage devices.
Furthermore, in the fibre channel switch, data may be copied between virtual storage devices.
Copy of data between virtual storage devices in the fibre channel switch is usually performed by DPCs (Data Path Controllers) of connection ports connected to fibre channels.
In a usual case, the fibre channel switch is provided with a plurality of connection ports and a plurality of DPCs, the number thereof being the same as the number of the connection ports.
Thus, when the number of copy sessions based on instructions from a host computer is equal to or larger than the number of DPCs, a copy process ability can be sufficiently ensured by efficiently assigning the copy sessions to the DPCs in the fibre channel switch (e.g., see Japanese Laid-open Patent Publication No. 2005-322230).
When the number of copy sessions is smaller than the number of DPCs in the fibre channel switch, a free DPC that does not perform a copy session exists. The existence of such a free DPC is inefficient, and the copy process ability can be further enhanced by effectively using the free DPC.